The bone healing process is influenced by various physiological factors. Fracture fixation traditionally relied on rigid metallic implants. However, excessively rigid constructs can lead to complications, necessitating revision surgery. This review focuses on approaches to improve bone healing by introducing adequate interfragmentary movement (IFM) at the fracture site. IFM promotes secondary fracture healing and callus formation. Studies suggest that rigid fixation may impair fracture healing by inhibiting callus formation and causing stress shielding. Titanium alloy locking plates have been shown to be biomechanically superior to stainless steel. Flexible fixation and techniques to regulate implant stiffness are crucial for managing fractures with bridge plating. Materials with a lower Young’s modulus balance biomechanical properties. A novel TiNbSn alloy with a low Young’s modulus has been developed to address stress shielding issues. It is effective in promoting osteosynthesis, bone healing, and superior mechanical properties compared with materials with higher Young’s moduli. The enhanced formation of bone and callus associated with TiNbSn alloy suggests its promise for use in fracture treatment plates. Understanding the biomechanics of fracture healing, optimizing fixation stiffness, and exploring innovative materials like TiNbSn alloys, are crucial for advancing approaches to accelerate and enhance bone healing.

Background: Ti6Al4V alloy, which is commonly used for biomedical applications, has a Young modulus (110 GPa) that is higher than that of human cortical bone (11 to 20 GPa). Using an implant with a material with a low Young modulus that enhances load sharing by the bone even more than those made of Ti6Al4V could be beneficial for bone healing and further reduce the potential for stress shielding. A new β-type TiNbSn alloy has a low Young modulus of approximately 40 to 49 GPa. However, whether the new titanium alloy with a lower Young modulus is advantageous in terms of fracture healing has not been assessed, and a small-animal model seems a reasonable first step in its assessment. Questions/purposes: To assess the impact of a TiNbSn alloy plate with a lower Young modulus compared with a Ti6Al4V alloy plate on fracture healing, we evaluated: (1) bony bridging and callus volume, (2) new bone formation and remaining cartilage tissue, (3) osteoblast activity in the callus, and (4) mechanical strength and stiffness of the callus in bending. Methods: Fracture plates manufactured from TiNbSn and Ti6Al4V alloys, which have Young moduli of 49 GPa and 110 GPa, respectively, were compared. The main reason for using rabbits was the high reliability of the three-point bending mechanical test of the rabbit tibia. Forty-two male Japanese white rabbits weighing 2.8 to 3.4 kg were anesthetized. A 5-cm skin incision was made on the medial side in the mid-diaphysis of the right tibia. Eight-hole plates were used, which were 42 mm long, 5 mm wide, and 1.2 mm thick. Plate fixation was performed using three proximal and three distal screws. After the plate was installed, an osteotomy was performed using a 1-mm-wide wire saw to create a standardized tibial transverse osteotomy model with a 1-mm gap. Bone healing was quantitatively assessed by two nonblinded observers using micro-CT (bony bridging and callus volume), histomorphometry (new bone formation and remaining cartilage tissue), immunohistochemistry (osteoblast activity), and mechanical testing (mechanical strength and stiffness in bending). Measurements on nondemineralized specimens were descriptive statistics due to their small number. Four weeks after osteotomy and fixation, 30 rabbits were euthanized to undergo micro-CT and subsequent mechanical testing (n = 12), histomorphometry and immunohistochemistry with demineralized specimens (n = 12), and histomorphometry with a nondemineralized specimen (n = 6). Eight weeks postoperatively, 12 rabbits were euthanized for micro-CT and subsequent mechanical testing. Results: Intramedullary fracture calluses treated with TiNbSn alloy plates had larger bone volumes and more numerous bridging structures than those treated with Ti6Al4V alloy plates at 4 weeks after osteotomy (Ti6Al4V alloy versus TiNbSn alloy: 30 ± 7 mm³ versus 52 ± 14 mm³, mean difference 22 [95% CI 9 to 37]; p = 0.005; ICC 0.98 [95% CI 0.95 to 0.99]). Histologic assessments demonstrated there was greater new bone formation (total callus: Ti6Al4V versus TiNbSn: 16 ± 4 mm² versus 24 ± 7 mm², mean difference 8 [95% CI 1 to 16]; p = 0.04; ICC 0.98 [95% CI 0.93 to 0.99]; intramedullary callus: Ti6Al4V versus TiNbSn: 6 ± 4 mm² versus 13 ± 5 mm², mean difference 7 [95% CI 1 to 13]; p = 0.02; ICC 0.98 [95% CI 0.95 to 0.99]) and a higher number of osteocalcin-positive cells (Ti6Al4V alloy versus TiNbSn alloy: 1397 ± 197 cells/mm² versus 2044 ± 183 cells/mm², mean difference 647 [95% CI 402 to 892]; p < 0.001; ICC 0.98 [95% CI 0.95 to 0.99]) in the TiNbSn alloy group than in the Ti6Al4V alloy group. At 4 weeks after osteotomy, both bone strength and stiffness of the healed bone in the TiNbSn alloy group were higher than those in the Ti6Al4V alloy group (maximum load: Ti6Al4V alloy versus TiNbSn alloy: 83 ± 30 N versus 127 ± 26 N; mean difference 44 [95% CI 8 to 80]; p = 0.02; stiffness: Ti6Al4V alloy versus TiNbSn alloy: 92 ± 43 N/mm versus 165 ± 63 N/mm; mean difference 73 [95% CI 4 to 143]; p = 0.047). Eight weeks after osteotomy, no between-group differences were observed in the strength and stiffness of the healed bone. Conclusion: The results of this study indicate that TiNbSn alloy plate with a lower Young modulus resulted in improved bone formation and stiffer callus during the early phase (4 weeks after surgery) but not the later phase (8 weeks after surgery) of bone healing. Clinical Relevance: An overly stiff plate may impair callus formation and bone healing. The TiNbSn alloy plate with a low Young modulus improves the early formation of new bone and stiff callus at the osteotomy site compared with the Ti6Al4V alloy plate in the healing process, which may promote bone repair. TiNbSn alloy may be a promising biomaterial for fracture treatment devices. Further research to address concerns about the strength of TiNbSn alloy plates, such as fatigue life and plate fracture, will be necessary for clinical applications, including mechanical tests to verify fatigue life and validation in larger animals with greater body weight.

Stress shielding remains a major concern in cementless total hip arthroplasty (THA) due to the stiffness mismatch between femoral stems and surrounding bone. This study investigated the biomechanical and clinical performance of a novel Ti-33.6Nb-4Sn (Ti-Nb-Sn) alloy stem with a graded Young’s modulus achieved through localized heat treatment. A finite element model (FEM) of the Ti-Nb-Sn stem, incorporating experimentally validated Young’s modulus gradients, was constructed and implanted into a patient-specific femoral model. Stress distribution and micromotion were assessed under physiological loading conditions. Clinical validation was performed by evaluating radiographic outcomes at 1 and 3 years postoperatively in 40 patients who underwent THA using the Ti-Nb-Sn stem. FEM analysis showed low micromotion at the proximal press-fit region (4.89 μm rotational and 11.74 μm longitudinal), well below the threshold for osseointegration and loosening. Stress distribution was concentrated in the proximal region, effectively reducing stress shielding distally. Clinical results demonstrated minimal stress shielding, with no cases exceeding Grade 3 according to Engh’s classification. The Ti-Nb-Sn stem with a gradient Young’s modulus provided biomechanical behavior closely resembling in vivo conditions and showed promising clinical results in minimizing stress shielding. These findings support the clinical potential of modulus-graded Ti-Nb-Sn stems for improving implant stability in THA.

TiNbSn alloy is a high-performance titanium alloy which is biosafe, strong, and has a low Young’s modulus. TiNbSn alloy has been clinically applied as a material for orthopedic prosthesis. Anodized TiNbSn alloys with acetic and sulfuric acid electrolytes have excellent biocompatibility for osseointegration. Herein, TiNbSn alloy was anodized in a sulfuric acid electrolyte to determine the antimicrobial activity. The photocatalytic activities of the anodic oxide alloys were investigated based on their electronic band structure and crystallinity. In addition, the cytotoxicity of the anodized TiNbSn alloy was evaluated using cell lines of the osteoblast and fibroblast lineages. The antimicrobial activity of the anodic oxide alloy was assessed according to the ISO 27447 using methicillin-susceptible Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, and Escherichia coli. The anodic oxide comprised rutile and anatase titanium dioxide (TiO₂) and exhibited a porous microstructure. A well-crystallized rutile TiO₂ phase was observed in the anodized TiNbSn alloy. The methylene blue degradation tests under ultraviolet illumination exhibited photocatalytic activity. In antimicrobial tests, the anodized TiNbSn alloy exhibited robust antimicrobial activities under ultraviolet illumination for all bacterial species, regardless of drug resistance. Therefore, the anodized TiNbSn alloy can be used as a functional biomaterial with low Young’s modulus and excellent antimicrobial activity.

Background and objectives: The superior placement of the acetabular cup induced the delayed recovery of abductor muscle moment after total hip arthroplasty (THA) with a conventional posterior approach. The anterior-based muscle-sparing (ABMS) THA effectively reduces soft tissue damage, including muscles. The influence of hip center position on anterior-based muscle-sparing (ABMS) total hip arthroplasty (THA) for post-operative hip muscle strength was unclear. We evaluate whether the hip center position affects the recovery of hip muscle strength after ABMS THA. Materials and Methods: The study was performed as a retrospective cohort study, and included 38 hips in 38 patients that underwent primary ABMS THA. Muscle strength was measured using isokinetic dynamometry before the operation, and at 6 and 12 months after surgery. The horizontal and vertical centers of rotation (H-COR and V-COR), vertical shift (V-shift), leg length, and global femoral offset were determined radiographically in reference to a previous report. Results: A weak negative correlation was observed between abduction muscle strength at 6 months and V-shift; a V-shift more than 15 mm demonstrated significantly decreased abductor muscle strength at 6 months. Conclusions: The superior placement of the hip center caused delayed recovery of abductor muscle strength in hips with anterolateral minimally invasive THA. There seems to exist no biomechanical reason why the same should not also be the case for the muscle-sparing approach.